One type of circuitry device is a field effect transistor. Typically, such includes opposing semiconductive material source/drain regions of one conductivity type having a semiconductive channel region of opposite conductivity type therebetween. A gate construction is received proximate the channel region, typically between the source/drain regions. The gate construction typically includes a conductive region having a thin dielectric layer positioned between the conductive region and the channel region. Current can be caused to flow between the source/drain regions through the channel region by applying a suitable voltage to the conductive portion of the gate.
Typical transistor fabrication methods include a step referred to as source/drain re-oxidation. Such may be conducted for any of a number of reasons depending upon the materials, sequence and manner by which transistor components have been fabricated prior to the re-oxidation step. For example, one method of providing a gate dielectric layer is to thermally grow an oxide over a bulk or semiconductor-on-insulator substrate. In certain instances, source/drain regions are provided by conducting ion implantation through this oxide layer after the gate construction has been patterned to at least partially form the source/drain regions. The heavy source/drain implant is likely to damage and contaminate the oxide remaining over the source/drain regions. Even if all the oxide were removed over the source/drain regions prior to the implant, damage to the crystal lattice and the source/drain outer surface typically occurs from the source/drain implant(s). Accordingly and regardless, a re-oxidation step is conducted to grow a fresh, uncontaminated oxide on the source/drain regions towards repairing certain damage caused by the implant. This typically occurs after any remaining damaged oxide has been stripped from over the source/drain regions.
Typically, this re-oxidation also grows a very thin thermal oxide on tops and sidewalls of the conductive components of the gate construction. Further, it tends to slightly thicken the gate oxide under the gate corners, and thereby round the lower outer edges of the typical polysilicon material of the gate. The ion implantation and any oxide stripping can weaken or mechanically compromise the gate oxide at the sidewall edges of the gate, and tend to increase the field effect transistor gate-to-drain overlap capacitance. The thickening and rounding of the gate oxide at the corners can reduce gate-to-drain overlap capacitance, and relieve the electric-field intensity at the corner of the gate structure, thus enhancing the gate oxide integrity at its edge. Further, the thermal oxide can serve as a dopant diffusion mask preventing dopant diffusion from subsequently deposited insulative interlevel dielectric layers.
However in many instances, it is desirable that none or a minimum of certain conductive materials of the transistor gates be oxidized. For example, one presently employed gate construction uses polysilicon, tungsten nitride and elemental tungsten as conductive materials. When using steam as a source/drain re-oxidant, the conditions would also tend to significantly oxidize the elemental tungsten. A prior art technique to minimize the effective formation of tungsten oxide on the tungsten is to provide H2 in combination with steam in the oxidizing atmosphere. The H2 tends to reduce the tungsten oxide back to tungsten, thus reducing or minimizing the amount of tungsten oxide which forms on the sidewalls of the tungsten material.
Some of the tungsten oxide which forms is in the vapor phase, with the oxidation/reduction reaction essentially being one of equilibrium with H2 and H2O. Unfortunately, tungsten oxide tends to deposit on internal reactor surfaces largely at the conclusion of the source/drain re-oxidation. Such requires periodic cleaning of the internal reactor components, thus reducing production time of the reactors. One prior art technique for increasing the time between cleanings is to reduce flow of steam to the reactor prior to reducing flow of the H2.
The invention was motivated in addressing the above described issues, but however is in no way so limited. The invention is only limited by the accompanying claims as literally worded (without interpretative or other limiting reference to the above background art description, remaining portions of the specification or the drawings) and in accordance with the doctrine of equivalents.